Methylcobalamin (Methyl-B12)

THIS IS A VITAMIN, NOT A PEPTIDE. Methylcobalamin is one of the active coenzyme forms of vitamin B12: a cobalt-centred corrinoid, with no amino acids and no peptide bonds anywhere in it. It is in this library because it is sold alongside peptides and blended into peptide products, not because it belongs to the same class of molecule, and nothing about the rest of the library should be read as implying otherwise. What it actually does is defined by deficiency.

B12 is the cofactor for methionine synthase and methylmalonyl-CoA mutase; a deficiency causes megaloblastic anemia and a peripheral and central neuropathy that can become irreversible, and correcting it is genuinely effective and cheap. In people who are NOT deficient, the evidence that extra B12 improves energy, mood or cognition is weak, and the large homocysteine-lowering trials with B vitamins did not translate into the cardiovascular or dementia benefits people expected.

Testing serum B12 (with methylmalonic acid or homocysteine where the result is borderline) before dosing is the honest first step. The methyl form is often marketed as superior to cyanocobalamin; head-to-head human evidence for that is thin. Cyanocobalamin is the better-characterized and cheaper form, is what most approved injectable and nasal-spray products contain, and works in almost everyone. Methylcobalamin is preferred mainly on theoretical grounds and in specific settings such as cyanide handling or tobacco amblyopia.

Dosing: 1000 mcg intramuscularly is the conventional injection dose, given on a loading schedule then monthly to three-monthly for maintenance in deficiency; the weekly default here reflects common self-directed practice, not a deficiency-treatment protocol. High oral doses of 1000-5000 mcg work even in pernicious anemia through passive diffusion that does not need intrinsic factor. Japanese trials in ALS and diabetic neuropathy have used far higher doses (25-50 mg, i.e.

25,000-50,000 mcg intramuscularly), which is well outside the range above and outside self-directed use. B12 has no established toxic upper limit and excess is renally cleared, which is why no contraindication flags are set; that is a statement about safety, not about efficacy. Serum half-life is not a useful number here because the body stores several years of B12 in the liver, so no figure is listed. Reconstitution fields are omitted: it is supplied as a ready-made solution ampoule or vial, a tablet or a sublingual product, never as a lyophilized powder you make up.

Methylcobalamin is strongly light-sensitive and must be kept in its amber container.